Integrated circuits (ICs) generate heat. To help prevent excessive operating temperatures, the heat can be dissipated through a thermal pathway including an IC package that houses the IC. Packages used in avionics or space applications are typically cooled by conduction from the bottom of a package into a printed wiring board (PWB).
Many high pincount IC packages use pins or balls on the bottom of a package for electrical connection to a PWB, which increases the thermal resistance between the package and the PWB compared to perimeter leaded packages with full bottom side contact to the PWB. Furthermore, as PWB complexity increases, the number of layers in the PWB increases, and the heat from the IC package is conducted through multiple layers (often through vias) before being conducted to the edge of the PWB, which further increases the thermal resistance of this conduction path. To alleviate these problems, emerging hardware designs attempt to remove heat from the top of the package through heat sinks, heat pipes, cooling plates, or other thermally conducting structures.
Standard hermetically-sealed ceramic packages used in avionics or space applications have a high thermal resistance or a poor thermal conduction path from the IC to the top side of the package. A large air gap also exists between the IC and the lid, further impeding heat conduction. Generally, the only conduction path to the top of the package is laterally through the package to the lid, and laterally across the lid.